Piezoactuator and a method for producing a piezoactuator

ABSTRACT

The invention relates to a piezoactuator ( 1 ) comprising a piezoelectric body ( 4 ) and elements for pre-tensioning the piezoelectric body, consisting of a first ( 2 ) and a second ( 3 ) connecting element for transferring forces to the piezoelectric body ( 4 ). The actuator is provided with an element ( 6 ) for transferring tensile/pressure forces between the connecting elements ( 2, 3 ), said element being at least partially located in a gap ( 5 ) in the form of a bore in the piezoelectric body ( 4 ). According to the invention, the piezoactuator ( 1 ) is set to a defined working curve using the pre-tensioning elements ( 2, 3, 6 ). The piezoelectric body ( 4 ) is preferably produced by the lamination of piezoelectric layers, into which a gap is drilled after lamination and the component is subsequently sintered.

The invention relates to a piezoactuator with a piezoelectric body andelements for pre-tensioning the piezoelectric body, said elementsconsisting of a first and a second connecting element for transferringforces to the piezoelectric body, and an element for transferringtensile/pressure forces between the connecting elements, said elementbeing disposed at least partially in a gap shaped in the form of a borein the piezoelectric body. The invention relates furthermore to a methodfor producing a piezoactuator having a piezoelectric body with a gapshaped in the form of a bore.

A piezoactuator of this type and a production method of this type aredisclosed in German Patent No. 198 14 697, which describes apiezoactuator comprising a piezoceramic body fashioned in the form of acylinder, said piezoceramic body consisting of a piezoceramic multilayerwhich is helical in structure. This piezoceramic body has a centralthrough bore serving to accommodate a mechanical clamping device, bymeans of which the piezoelectric body can be braced parallel to thecylinder axis between two terminal plates serving as connecting elementsfor transferring forces to the piezoelectric body. The respectiveterminal plates are connected with one another via a bar-shapedretaining element in which it is possible for a bore for conducting acooling liquid to be provided.

In the method for producing a piezoactuator of this type, a hollowpiezoceramic cylinder is initially furnished with cut surfaces runningin the form of joined helices, into which cut surfaces electrodematerial is inserted in a subsequent process step. It is proposed as avariant of this production method that a cylinder be processed fromelectrode material, that helical cut surfaces be incorporated into thiscylinder and that these cut surfaces then be filled with piezoceramicmaterial.

The object of the invention is to create a piezoactuator with a lowinherent spatial requirement, which piezoactuator will upon applicationof an electrical potential provide a precisely defined deflection of adrive unit.

This object is achieved by the piezoactuator according to claim 1.Further features, aspects, advantages and details of the invention willemerge from the dependent claims, the description and the drawings.Advantages, features and details of the invention which are described inrelation to the piezoactuator will of course also apply to the methodfor producing a piezoactuator, and vice versa.

According to a first aspect of the invention, a piezoactuator of thetype specified in the introduction is further developed in such a waythat this piezoactuator is set to a defined working curve using thepre-tensioning elements.

It is in this way possible, given a piezoactuator of the same type ofconstruction, to set this piezoactuator for different applications.Efficient piezoactuator modules can be created with integratedpre-tensioning and low installation space requirements. The design ofthe piezoactuator according to the invention makes it possible,depending on the particular design, to implement, for example, adisplacement reversal, a defined setting of a working curve as afunction of temperature, a defined setting of the absolute length of themodule as a function of temperature (or temperature compensation), aforce-displacement transformation and such like. Non-exclusive examplesof these will be explained in greater detail in the further course ofthe description.

In a development of the invention, the piezoactuator has a mounting padsection which is rigidly connected with the piezoelectric body. In thisway, a piezoactuator with a servo drive which moves relative to themounting pad section will be created.

The piezoelectric body is advantageously designed as a monolithicpiezoceramic multilayer actuator. In this way, a piezoactuator iscreated which can be economically produced. Piezoceramic multilayeractuators generally consist of a large number of alternately arrangedceramic layers and metal internal electrodes.

Preferably at least one connecting element for transferring forces tothe piezoelectric body is designed as a clamping plate. This enables agood transfer of forces between the connecting element and thepiezoelectric body. At high clamping forces an adequately rigidconnection of the element for transferring tensile/pressure forces withthe clamping plates can advantageously, but not exclusively, be achievedvia a welded connection. Simultaneously and/or alternatively, theclamping plates can be designed appropriately both in terms of materialand in terms of plate strength.

In a development of the invention, the element for transferring forcesbetween the connecting elements is designed in the form of a solidprofile. In this way, large forces can be transferred, adjustment of therigidity of the element for transferring forces enabling precisedetermination of the working point of the piezoactuator in theforce-displacement diagram.

The element for transferring forces between the connecting elements isadvantageously designed in the form of a hollow profile.

In a further embodiment, a medium for cooling and/or thermostaticregulating can be provided or carried in the hollow profile. In this wayit is possible to cool or to thermostatically regulate the piezoactuatorusing a coolant conducted through the hollow profile. Cooling of thepiezoactuator is particularly suitable for highly dynamic control in thelarge-signal range. Thermostatic regulation is advantageous, forexample, when a precisely settable and reproducible deflection isrequired.

A drive element of the piezoactuator is preferably accommodated in thehollow profile of the element for transferring forces between theconnecting elements. In this way, reversal of the displacement of thedrive unit of the piezoactuator can be achieved relative to theexpansion of the piezoelectric body in the piezoactuator.

A thermal coupling medium can advantageously be provided at least inareas between the pre-tensioning elements and the piezoelectric body.Through thermal coupling, at least in areas, via the coupling medium,heat generation, heat injection, heat dissipation and the like can becontrolled in a targeted directed and defined manner. The thermalcoupling medium can, for example, be a plastic, a fluid or the like. Theeffectiveness of the cooling and/or thermostatic regulating, asdescribed further above, can be increased further, for example, byintroducing a thermal coupling medium between the hollow profile and thesurface of the actuator.

In a further embodiment, the thermal expansion of the elements forpre-tensioning the piezoelectric body matches the thermal expansion ofthe piezoelectric body. In this way, by purposefully matching thethermal expansion coefficients of the piezoelectric body and of thepre-tensioning elements, a defined change in the displacement of thepiezoactuator as a function of temperature is adjustably maintained.

The ceramics used for piezoactuators generally exhibit thermal expansioncoefficients which deviate greatly from commonly used metals. Thethermal expansion coefficients of the elements for pre-tensioning thepiezoelectric body can, for example, through the appropriate selectionof material, adaptation of the design (such as the strength, thelaminate structure and the like) and the like be set so that the thermalexpansion of the piezoactuator as a whole can be tailored precisely forthe application concerned.

In a further embodiment, the rigidity of the elements for pre-tensioningthe piezoelectric body can be matched to a required working point of thepiezoactuator in the working curve. This can be achieved, for example,though not exclusively, through appropriate selection of the material,selection of the cross-section, configuration or construction of thepre-tensioning elements or parts thereof, in particular of the elementfor transferring tensile/pressure forces, as a laminate body and thelike.

If, for example, a defined working curve is required in theforce/displacement diagram as a function of temperature (that is, atargeted displacement change as a function of temperature), then thiscan be achieved by selectively combining the thermal expansioncoefficients and the rigidity of the pre-tensioning elements.

The elements for pre-tensioning the piezoelectric body preferablycomprise a cup spring. In a further embodiment, the elements forpre-tensioning the piezoelectric body can comprise a helical spring. Inthis way, through targeted selection of the temper of the spring, adefined working displacement and working point of the piezoactuator canbe adjustably maintained.

It is advantageous to provide at least one further element forfrictionally connecting the first and second connecting element fortransferring forces to the piezoelectric body. In this way, solid statejoints are created on the connecting elements, which solid state jointsenable a curved working traverse of a drive unit of the piezoactuator,wherein a lever action can be utilized for the working displacement.

According to a second aspect of the invention, a method for producing apiezoactuator, in particular a piezoactuator as described hereinaboveaccording to the invention, is provided, in which method a piezoelectricbody is produced by laminating piezoceramic layers. A gap shaped in theform of a bore is drilled in this piezoelectric body after lamination.After the drilling process, the piezoelectric body is then sintered.After completion of the piezoelectric body, the piezoactuator is thenpre-tensioned using elements for pre-tensioning the piezoelectric body,said elements having a first and a second connecting element fortransferring forces to the piezoelectric body and an element fortransferring tensile/pressure forces between the connecting elements,said element being at least partially located in a gap shaped in theform of a bore in the piezoelectric body, the piezoactuator being set toa defined working curve using the pre-tensioning elements.

In this way, a piezoactuator is created, the piezoelectric body of whichhas a high electric flashover resistance and short-circuit strength. Atthe same time, the gap in the piezoelectric body of the piezoactuatorcan be produced to extremely precise dimensions. This production methodalso makes it possible for piezoactuators to be produced economically inlarge unit numbers.

Further features and advantages of the invention are shown in thedrawings and are described hereinbelow.

FIG. 1 is a sectional view of an embodiment of a piezoactuator with afirst and a second clamping plate;

FIGS. 2 and 3 are each sectional views of piezoactuators pre-tensionedby means of a cup spring;

FIG. 4 is a sectional view of a piezoactuator with a joining elementshaped in the form of a hollow profile between connecting elements fortransferring forces to a piezoelectric body; and

FIGS. 5, 6 and 7 are each sectional views of piezoactuators with solidstate joints.

The piezoactuator 1 shown in FIG. 1 has a first and a second clampingplate 2 and 3 which serve respectively as a first and second connectingelement for transferring forces to a piezoelectric body 4. Thepiezoelectric body 4 is constructed as a monolithic piezoceramicmultilayer actuator and has centrally a through-hole, circular incross-section, held as a gap shaped in the form of a bore 5. In this gap5 runs a metal bar 6 serving as an element for transferring forcesbetween the clamping plate 2 and the clamping plate 3 and holding thepiezoelectric body 4. The clamping plates 2 and 3 and the metal bar 6are designed for transferring high clamping forces to the piezoelectricbody, for example, for clamping forces in the region of 850 N.

The clamping plate 3 is fixed on a mounting pad section 7, by means ofwhich the piezoactuator 1 is fastened in an intended operating location.The piezoactuator 1 can receive an electrical signal via terminals forsupplying an electrical potential, which terminals are not describedfurther. This electrical signal results in an expansion or contractionof the piezoelectric body 4 corresponding to a movement indicated by thebidirectional arrows 8 and 9. Such a movement of the piezoelectric body4 is transferred to the clamping plate 2 which represents a drive unitfor a drive movement indicated by the bidirectional arrow 10.

The thermal expansion of the metal bar 6 is adapted here to the thermalexpansion of the piezoelectric body 4. This action can firstly achieve atemperature-independent working curve of the piezoactuator 1, whereinthe thermal expansion of the piezoelectric body 4 compensates for thethermal expansion of the metal bar 6 and of the clamping plates 2 and 3.However, it is also possible as an alternative to this action to selecta defined ratio of the thermal expansion of the metal bar 6 and thepiezoelectric body 4 such that a defined change can be achieved in theworking curve of the piezoactuator 1 as a function of temperature.

As well as through selection of the thermal expansion of the metal bar 6and of the piezoelectric body 4, the working curve of the piezoactuator1 can also be fixed by adjusting the mechanical tension loading betweenthe clamping plates.

This can be achieved, for example, by appropriate selection of thegeometric dimensions of the metal bar 6, the clamping plate 2, 3 and thepiezoelectric body before final assembly of the piezoactuator 1. Inorder to brace the clamping plates 2, 3 via the metal bar 6, suitablethreaded clamping units or equivalent means can, however, also beprovided in the components concerned.

In order to enable a force to be introduced evenly across the entireface of the piezoelectric body 4, the clamping plates 2 and 3 areadvantageously kept curved. Particularly large forces can be transferredbetween the metal bar 6 and the clamping plates 2 and 3 if the metal bar6 and the clamping plates 2 and 3 are connected by means of weldedjoints.

In the piezoactuator 20 shown in FIG. 2, a piezoelectric body 21 whichis provided with a through-hole implemented as a gap in the form of abore 22 is held on one side by a clamping plate 23 serving as a driveunit. On the other side, the piezoelectric body 21 is connected with abase element 25 shaped in the form of a hollow profile, which baseelement is fixed on a mounting pad section 26.

The piezoelectric body 21 is braced between the clamping plate 23 andthe base element 25 in the form of a hollow profile by the force of acup spring 27, the spring tension of which is transferred through ametal bar 28. By selecting the tensional force of the cup spring 27appropriately, it is possible to set any required working curve of thepiezoactuator 20 based on suitable pre-tensioning of the piezoelectricbody 21.

Applying a voltage to the piezoelectric body 21 via electrical terminalsnot described further causes an expansion or contraction movement of thepiezoelectric body corresponding to the movement indicated by thebidirectional arrows 29. This expansion or contraction of thepiezoelectric body 21 is transferred to the clamping plate 23 serving asa drive unit, which clamping plate then moves in accordance with thebidirectional arrow 24.

The thermal expansion of the metal bar 28, of the cup spring 27 and ofthe piezoelectric body 21 are in turn advantageously matched to oneanother.

Through appropriate selection of the spring temper of the cup spring 27and the specification of an appropriate pre-tensioning force for thepiezoelectric body 21 it is possible, as in the piezoactuator 1described by FIG. 1, to set a defined working curve.

In place of the cup spring 27, a helical spring or another suitablespring element can also be used.

The functional principle of the piezoactuator 30 shown in FIG. 3corresponds in principle to that of piezoactuator 20 from FIG. 2.However, the piezoactuator 30 has a cup spring 31 in order to brace apiezoelectric body 32 having a through-hole shaped as a gap in the formof a bore 33 between a clamping plate 34 and a mounting pad section 35via a metal bar 36. A working opening 37 is provided in the mounting padsection 35, through which opening the metal bar 36 juts so as toinitiate in a drive unit 38 a drive movement running in accordance withthe bidirectional arrow 39. The direction of this drive movement is thereversal of the displacement relative to the piezoactuator shown in FIG.2, that is, when the piezoelectric body 32 expands, the drive area movestoward the mounting pad section 35, and when the piezoelectric bodycontracts, the drive area moves by contrast away from this mounting padsection.

In contrast with this, an expansion of the piezoelectric body 21 inpiezoactuator 21 from FIG. 2 produces a displacement movement whichguides the clamping plate 23 serving as a drive mechanism away from themounting pad section, and produces conversely, when the piezoelectricbody 21 contracts, a movement in the direction of the mounting padsection 26.

It should be noted that, like the piezoactuator 20 from FIG. 2, thepiezoactuator 30 shown in FIG. 3 can also be constructed with helicalsprings or another suitable spring element in place of a cup spring. Asin the case of the piezoactuators shown in FIG. 1 and FIG. 2, thethermal expansion of the components of the piezoactuator 30 are in turnadvantageously matched to one another in order either to enable atemperature-independent working curve of the piezoactuator or to createa piezoactuator the working curve of which changes in a defined way as afunction of temperature. Furthermore, in conformity with the remarks inrelation to FIGS. 1 and 2, the working curve of the piezoactuator can beset in a defined way through appropriate pre-tensioning of thepiezoelectric body 32 using the clamping plate 34, the mounting padsection 35, the cup spring 31 and the metal bar 36.

FIG. 4 shows a piezoactuator 40 with a piezoelectric body 41 which, inturn, has a through-hole implemented as a gap shaped in the form of abore 42 and is braced between a first clamping plate 43 and a secondclamping plate 44 with a bar implemented in the form of a hollowprofile. The piezoelectric body 41 is fixed with the second clampingplate 44 on a mounting pad section 47 furnished with a through opening46. A drive rod 48 is provided in the piezoactuator 40 as a drive unit,which drive rod runs in the bar held in the form of a hollow profile 45,juts through the through opening 46 in the mounting pad section 47 andis fixed in the area of the first clamping plate 43. When there is adefined expansion or contraction of the piezoelectric body 41corresponding to a movement indicated by means of the bidirectionalarrows 49, a drive movement of the drive rod 48 is generated toward themounting pad section 47 or away from the mounting pad section inaccordance with the bidirectional arrow 49 a.

In order to counteract any rise in temperature of the piezoactuator 40during operation, there can be provision for introducing a cooling fluidin the hollow-profile form of the bar 45. The temperature of thepiezoactuator is then preferably regulated so as to enable preciselydefinable and reproducible deflections even for highly dynamic controlin the large-signal range.

As in the case of the piezoactuator shown in FIG. 3, however, a reversalof the displacement of the drive unit of piezoactuator 40 by comparisonwith the drive units of the piezoactuators from FIGS. 1 and 2 isachieved.

As far as the selection of the thermal expansion of the components usedand the mechanical pre-tensioning of the piezoelectric body 41 areconcerned, the explanations relating to FIGS. 1 to 3 should be referredto.

FIG. 5 shows a piezoactuator 50 which, like the piezoactuator describedpreviously, has a piezoelectric body 51 with a through-hole which isheld as a gap shaped in the form of a bore 52. The piezoelectric body 51is braced between a first clamping plate 53 and a second clamping plate54 via a bar 55 and is fixed on a mounting pad section 56. In addition,the first clamping plate 53 and the second clamping plate 54 areconnected via a connecting arm 57 which acts as a solid state joint inareas 58 and 59. When an electrical voltage is applied to thepiezoactuator 50 via electrical terminals which are not describedfurther, a contraction or expansion of the piezoelectric body 51 isgenerated, which contraction or expansion proceeds asymmetrically,however, because of the solid state joints in areas 58 and 59 so that inthe first clamping plate 53 serving as a drive unit a drive movementdescribing the form of an arc is produced, as indicated by means of thebidirectional arrow 59 c.

As far as the selection of the thermal expansion of the components usedand the mechanical pre-tensioning of the piezoelectric body 41 areconcerned, the explanations relating to FIGS. 1 to 3 should be referredto.

The piezoactuator 60 in FIG. 6 contains a piezoelectric body 61 which ismechanically braced by means of a first clamping plate 62, a secondclamping plate 63 and by means of connecting arms 64 and 65 runningoutside the piezoelectric body 61 and forming solid state joints 66 a,66 b, 66 c and 66 d.

The piezoelectric body 61 is fixed on a mounting pad section 67 via thesecond clamping plate 63. In piezoactuator 60 there is provided a bar 68which runs in a gap in the form of a bore fashioned as a through-hole 69in the piezoelectric body 61 and provides a drive movement in an area 69a serving as a drive unit. When an electrical potential is applied tothe piezoactuator 60, an uneven expansion corresponding to arrows 69 c,69 d, 69 e and 69 f is generated on account of the clamping of thepiezoelectric body 61 between the first clamping plate 62 and the secondclamping plate 63, which uneven expansion produces an arching of thefirst clamping plate 62. This results in a movement of the bar 68 in thearea 69 a in a manner as indicated by the bidirectional arrow 69 b.

A lever action of the selected first clamping plate 62 on the area 69 ais thus exploited for the movement of the area 69 a serving as a driveunit. This lever action enables a transformation of the expansion orcontraction movement of the piezoelectric body 61, i.e. the displacementof the area 69 a serving as a drive unit is increased relative to thedisplacement of the expansion or contraction movement of thepiezoelectric body 61.

As far as the selection of the thermal expansion of the components usedand the mechanical pre-tensioning of the piezoelectric body areconcerned, the explanations relating to FIGS. 1 to 3 should be referredto.

FIG. 7 shows a piezoactuator 70, the method of operation of whichmatches that of piezoactuator 60 from FIG. 6. The piezoactuator 70contains a piezoelectric body 71 which is enclosed and braced between afirst clamping plate 72 and a second clamping plate 73 via lateralclamping arms 74 and 75, forming solid state joints 76 a, 76 b, 76 c and76 d. In areas 77 and 78, the piezoelectric body 71 is held by aconnecting cover shaped in the form of a ring, the connecting coverbeing trapezoidal in cross-section, so as to ensure that, when thesurface of the connecting cover in contact with the first clamping plate72 is only limited, the clamping force passes symmetrically to thepiezoelectric body 71. In the piezoelectric body 71 there is provided agap 79 a held as a through-hole shaped in the form of a bore, which gapaccommodates a bar 79 b serving as a drive unit. If an electricalvoltage signal is applied to the piezoactuator 70 via electricalterminals not shown further causing an expansion or contraction of thepiezoelectric body 71, as indicated by the bidirectional arrows 79 e and79 f, relative to the mounting pad section 79 g, then the bar 79 bexecutes a drive movement, indicated by the bidirectional arrow 79 d, inan area 79 c.

As far as the selection of the thermal expansion of the components usedand the mechanical pre-tensioning of the piezoelectric body areconcerned, the explanations relating to FIGS. 1 to 3 should be referredto.

It is of course possible to modify the drive concept of thepiezoactuators from FIGS. 6 and 7 to the effect that a drive occurs witha reversal of displacement relative to the expansion and contraction ofthe piezoelectric body, as has been explained for piezoactuators 30 and40 using FIGS. 3 and 4.

The piezoelectric body of the piezoactuators shown in FIGS. 1 to 7 canbe implemented in cylindrical form but can also be fashioned intrapezoid form, cuboid form or with an ellipsoidal cross-section.Instead of keeping the through-hole passing through the piezoelectricbody circular, it is also possible to provide a cross-section in theform of a rectangle, for example a square cross-section. In general, thetensioning of the piezoelectric body is selected such that thepiezoactuator has a working curve which is favorable for its use. Theelastic and thermoelastic properties of the material used, in particularof the piezoelectric bodies and the clamping devices are matched to oneanother for this purpose.

By providing cooling means for a piezoactuator, it is possible virtuallyto exclude temperature effects on any drive movement provided.Particularly precise drive movements can be achieved with apiezoactuator which is operated at a regulated temperature.

The piezoelectric body in the piezoactuators shown in FIGS. 1 to 7 canbe implemented as a sintered ceramic, the gap in it in the form of abore being created by means of drilling. There is always the risk herethat insulating layers located on the piezoelectric body will be damagedin the area of the clamping plates, which damage can not least resultalso in an inhomogeneous distribution of the clamping forces. It mustalso be expected that in the drilling process in the area of the gapshaped in the form of a bore material from internal electrodes locatedthere will be smeared solidly over the interior surface of the bore.This can lead in subsequent electrical operation of the piezoelectricbody to the occurrence of flashovers and short circuits.

If, by contrast, multilayer components are used as piezoelectric bodies,then because of their low resistance to delamination cracks, lowfeedrates must be operated at when they are being processed, and thereis the risk that if rinsing water and boring dust is inadequatelyremoved, excess mechanical tensions will occur leading to destruction ofthe component through cracking.

It is, however, advantageous to produce the piezoelectric body in thepiezoactuator shown in FIGS. 1 to 7 from a piezostack which is still ina green state, i.e. is mechanically processed immediately afterlamination of the stack. The through boring in the respectivepiezoelectric bodies can be carried out using normal twist drills, withcooling and lubrication of the drill being unnecessary because thematerial is still soft. Because of the softness of the material thepressure on the drill required to achieve an adequate feedrate can alsobe kept low. If, in addition, drilling base plates are used in thedrilling process, no chipping will occur. While the drilling processalso produces in these piezoelectric bodies smearing of metal internalelectrodes which can be implemented, for example, as internal Ag/Pdelectrodes, in subsequent sintering of the component these smears,particularly the silver constituent, diffuse into the component and areeliminated with the formation of an as-fired sintered surface. Thesintered component can then be processed further without any requirementfor post-processing in the area of the through-hole. This then providesadequate flashover resistance and short-circuit strength in this areadirectly. Instead of producing the through-hole using a drill, there isin principle also the possibility of processing the raw piezoelectricbody using turning, milling and similar methods. This green processingmethod enables in particular, the efficient production of very largeunit numbers of blanks of a piezoelectric body which is outstandinglysuitable for use in a piezoactuator as shown in FIGS. 1 to 7.

1. A piezoactuator comprising a piezoelectric body in the form of amonolithic piezoceramic multilayer actuator; and elements forpre-tensioning the piezoelectric body, comprising a first and a secondconnecting element for transferring forces to the piezoelectric body;and an element for transferring tensile/pressure forces between theconnecting elements, said element being at least partially disposed in agap shaped in the form of a bore in the piezoelectric body, wherein thepiezoactuator is set to a defined working curve using the pre-tensioningelements, characterized in that to set the defined working curve,thermal expansion of the piezoelectric body and thermal expansion of thepre-tensioning elements are matched to one another; and wherein themember for transferring forces between the connecting elements isconstructed in the form of a hollow profile.
 2. A piezoactuatoraccording to claim 1, wherein the piezoactuator has a mounting padsection with which the piezoelectric body is rigidly connected.
 3. Apiezoactuator according to claim 1, wherein at least one connectingelement for transferring forces to the piezoelectric body is constructedas a clamping plate.
 4. A piezoactuator according to claim 1, whereinthe member for transferring forces between the connecting elements isconstructed in the form of a solid profile.
 5. A piezoactuator accordingto claim 1, wherein a medium for cooling and/or thermostatic regulatingis provided or is carried in the hollow-profile form.
 6. A piezoactuatoraccording to claim 1, wherein a drive element of the piezoactuator isaccommodated in the hollow-profile form of the element for transferringforces between the connecting elements.
 7. A piezoactuator according toclaim 1, wherein the thermal expansion of the elements forpre-tensioning the piezoelectric body corresponds to the thermalexpansion of the piezoelectric body.
 8. A piezoactuator according toclaim 1, wherein the rigidity of the elements for pre-tensioning thepiezoelectric body is matched to a required working point of thepiezoactuator in the working curve.
 9. A piezoactuator according toclaim 1, wherein the elements for pre-tensioning the piezoelectric bodycomprise a cup spring.
 10. A piezoactuator according to claim 1, whereinthe elements for pre-tensioning the piezoelectric body comprise ahelical spring.
 11. A piezoactuator according to claim 1, furthercomprising at least one further element for frictionally connecting inthe first and second connecting element for transferring forces to thepiezoelectric body.
 12. A piezoactuator comprising a piezoelectric bodyin the form of a monolithic piezoceramic multilayer actuator; andelements for pre-tensioning the piezoelectric body, comprising a firstand a second connecting element for transferring forces to thepiezoelectric body; and an element for transferring tensile/pressureforces between the connecting elements, said element being at leastpartially disposed in a gap shaped in the form of a bore in thepiezoelectric body, wherein the piezoactuator is set to a definedworking curve using the pre-tensioning elements, characterized in thatto set the defined working curve, thermal expansion of the piezoelectricbody and thermal expansion of the pre-tensioning elements are matched toone another; and wherein a thermal coupling medium is provided at leastin areas between the pre-tensioning elements.